1. Field of the Invention
The present invention relates generally to Power over Ethernet (PoE) and, more particularly, to a system and method for global power management in a PoE chassis.
2. Introduction
The IEEE 802.3af and 802.3at PoE specifications provide a framework for delivery of power from power sourcing equipment (PSE) to a powered device (PD) over Ethernet cabling. Various types of PDs exist, including voice over IP (VoIP) phones, wireless LAN access points, network cameras, computing devices, etc.
In the PoE process, a valid device detection is first performed. This detection process identifies whether or not it is connected to a valid device to ensure that power is not applied to non-PoE capable devices. After a valid PD is discovered, the PSE can optionally perform a power classification. In 802.3af, the power classification process can be used to classify a PD into various pre-defined power levels (i.e., 4.0 W, 7.0 W, and 15.4 W). In more advanced power classification schemes, a dynamic power management process can be used to generate a power request and priority for a PD based on current or anticipated power needs. As the total PSE power budget is typically limited as compared to the total power demand of the set of PDs, the dynamic power management process would consider the competing power needs of the various PDs.
The goal of the PSE management task is to provide stable output power to the various PDs. There are different PoE power supplies schemes used in the industry. Many stackable switches use a 1+1 redundant system for PoE using O ring diodes in which case available power is only limited to one power supply. In chassis based switches, on the other hand, N+1 redundancy enables current sharing in which case available power is N and one power supply is used for back up purpose. This additional power supply comes at significant cost. What is needed therefore is a mechanism that enables protection from power supply failures without incurring the cost of redundant power supplies.